DETECTION OF A NEW INTERSTELLAR MOLECULAR ION, H2COH+ (PROTONATED FORMALDEHYDE)

A new interstellar molecular ion, H2COH+ (protonated formaldehyde), ha s been detected toward Sgr B2, Orion KL, W51, and possibly in NGC 7538 and DR21(OH). Six transitions were detected in Sgr B2(M). The 1(1,0)- 1(0,1) transition was detected in all sources listed above, Searches w ere also made toward the cold, dark clouds TMC-1 and L134N, Orion (3N, 1E), and a red giant, IRC +10216, without success. The excitation tem peratures of H2COH+ are calculated to be 60-110 K, and the column dens ities are on the order of 10(12)-10(14) cm(-2) in Sgr B2, Orion KL, an d W51. The fractional abundance of H2COH+ is on the order of 10(-11) t o 10(-9), and the ratio of H2COH+ to H2CO is in the range 0.001-0.5 in these objects. The values in Orion KL seem to be consistent with the ''early time''-values of recent model calculations by Lee, Bettens, & Herbst, but they appear to be higher than the model values in Sgr B2 a nd W51 even if we take the large uncertainties of column densities of H2CO into account. We suggest production routes starting from CH3OH ma y play an important role in the formation of H2COH+.